There have been various known techniques of restraining occupants of motorcycles with airbag apparatuses. For example, known techniques include a technique of restraining an occupant with an airbag inflated by inflation gas in a frontal collision (e.g., refer to Japanese Unexamined Patent Application Publication No. 2003-327182). The airbag apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2003-327182has a structure in which a prefolded airbag is housed in a housing and in which an airbag opening of the housing is covered with an airbag cover (covering member). The airbag cover is torn open along a fragile portion with the deploying motion of the airbag to open the airbag opening, thereby enabling the deploying motion of the airbag from the interior of the housing to the exterior.
In the airbag apparatus described in Japanese Unexamined Patent Application Publication No. 2003-327182, water or oil may flow into the airbag housing through a hole or opening of the airbag cover from the exterior. For example, when a tether is employed for tethering the airbag to the vehicle body, the airbag cover has a tether through hole for the tether to pass through so that the tether extending from the housing through the upper part of the housing wall extends to the outside of the airbag cover. With this arrangement, liquid such as water or oil may enter the housing through the tether through hole from the exterior of the airbag cover. Particularly, general motorcycles have an airbag apparatus exposed to the outside of the body in contrast to cars, so that this problem may be pronounced under the influence of rain, cleaning water, and humidity.